What? When? How?

When the handle broke off a jug I was reminded of an episode of QI, in which the origin of the question mark was explained. They said it was derived from the Latin, where the word 'quaestio' was added at the end of an interrogative sentence, reduced in the written form to the letters qo, corrupted in time to the symbol we now use in the English language. It sounded quite plausible.

However, when  I looked online to provide a link I appear to have opened a whole can of worms. I would not dare to contradict the boffins of the QI research department, but according to Wikipedia this may be only one suggestion among many, which I do not begin to understand.

Which derivation do you favour?